The present invention relates to a cam unit for converting a rotary motion into a reciprocative motion, and also relates to a sewing machine employing the cam unit.
FIG. 4 shows the constitution of a conventional differential vertical sewing machine in which a main shaft 1 is supported by bearings 1a and 1b so that the shaft is rotated by a motor not shown in the drawing. The left-hand end of the main shaft 1 is coupled to a needle rod and thread take-up mechanism 12 made of a needle rod 13 and a thread take-up lever 14. The needle rod 13 is guided by bearings 13a and 13b. A flywheel 1c is mounted on the main shaft 1 at the right-hand end thereof. Four eccentric wheels 4, 6, 8 and 10 for causing an upper feed vertical driving force (i), an upper feed horizontal driving force (ii), a lower feed vertical driving force (iii) and a lower feed horizontal driving force (iv), respectively, and a bevel gear 2 for transmitting the torque of the main shaft 1 to a lower shaft 18 are attached to the central portion of the main shaft. The lower shaft 18 is rotatably supported by bearings 18a and 18b. A bevel gear 17 and a shuttle hook 19 are attached to the lower shaft 18 at the right-hand end and left-hand end thereof, respectively. A vertical shaft 15 is supported by bearings 15a and 15b. Bevel gears 3 and 16 are mounted on the vertical shaft 15 a the upper and lower ends thereof, respectively, and engaged with the bevel gears 2 and 17, respectively. An upper feed shaft 38 is rotatably supported by bearings 38a and 38b. The input portion 38i of the upper feed shaft 38 at the right-hand end thereof is coupled to an upper feed quantity controller 20 by a pin 24. The output portion 38o of the shaft 38 at the left-hand end thereof is split into two parts and surrounds a member 39 rotatably supported by the input end portion of a horizontal driving lever 40. An upper feed dog 55 is provided with upper feed teeth 57 at the front end of the dog and is rotatively coupled at the rear end of the dog to the lower end of the horizontal driving lever 40. The two-split front portion of the upper feed dog 55 surrounds a cam follower 50 rotatably supported on a rod 49b at the lower end thereof. The rod 49b is slidably supported by the body 53 of a head. A driving lever 45 is rotatably supported at the central portion thereof. A cam follower 46 is attached to the driving lever 45 at the output portion thereof. The lever 45 is rotatively coupled at the input portion thereof to a rod 5 at the lower end thereof. The rod 5 is rotatively coupled at the upper end thereof to the eccentric wheel 4. An upper feed vertical motion lever 49a shaped as L is rotatably supported by a lifter attaching rod 52 supported by the head body 53 so as to be vertically slidable. The vertical portion of the lever 49a is engaged with the cam follower 46. The horizontal portion of the lever 49a is engaged with the bottom of the upper horizontal portion of the rod 49b. A rod 7 is rotatively coupled at the upper portion thereof to the eccentric wheel 6, and coupled at the lower end portion of the rod to the upper feed quantity controller 20. The controller 20 includes a control lever 25, an auxiliary lever 27 and a coupling lever 28 which are supported to be tunable about the axis of the fixed shaft 21 secured to the head body 53, a pin 22 for rotatively coupling the control lever and the auxiliary lever to each other, a pin 23 for rotatively coupling the auxiliary lever and the coupling lever to the rod 7 at the lower end thereof, and a pin 24 for rotatively coupling the coupling lever to the input portion 38i of the upper feed horizontal motion shaft 38. A lower feed horizontal motion shaft 58 is rotatably supported by bearings 58a and 58b and coupled at the input portion 58i of the shaft to a lower feed quantity controller 29. The output portion 58o of the shaft 58 is rotatively coupled to a feed dog 59 at the rear end thereof. The feed dog 59 has feed teeth 25 on the central part of the portion. The front end portion 59o of the dog 59 is split into two parts. A lower feed vertical motion shaft 62 is rotatably supported by bearings 62a and 62b, and rotatively coupled at the output portion 62o of the shaft to a member 60. The output portion 62o of the shaft 62 is surrounded by the two-split portion of the feed dog 59. The input portion 62i of the shaft 62 is rotatively coupled to a rod 9 at the lower end thereof. The upper portion of the rod 9 is rotatively coupled to the eccentric wheel 8. A rod 11 is rotatively coupled at the upper portion thereof to the eccentric wheel 10 and coupled at the lower end of the rod to the lower feed quantity controller 29. The controller 29 includes a control lever 34, an auxiliary lever 36 and a coupling lever 37 which are supported to be tunable about the axis of the fixed shaft 30 secured to the head body 53, a pin 31 for rotatively coupling the control lever and the auxiliary lever to each other, a pin 32 for rotatively coupling the auxiliary lever and the coupling lever to the road 11 at the lower end thereof, and a pin 33 for coupling the coupling lever to the input portion of the lower feed horizontal motion shaft 58.
FIG. 5 shows an enlarged partial view of another conventional differential vertical sewing machine of such kind at and near a lower feed dog 59. The difference of the machine from that shown in FIG. 4 is that a two-split vertical driving lever 63 is secured to a lower feed vertical motion shaft 62 at the tip thereof and surrounds a member 60 rotatably supported by the lower feed dog 59 at the tip thereof.
FIG. 6 shows an enlarged partial view of another conventional differential vertical sewing machine at and near a lower feed dog 59. In the machine, a lower feed vertical motion shaft 62 is rotated, as differs from those shown in FIGS. 4 and 5, a cam 63 is secured to the shaft at the tip thereof, a cam follower 60 is attached to the portion of the lower feed dog 59, which is engaged with the cam, and a spring 67 engaged with the body of a head and a spring attaching member 71 provided on the dog at the tip thereof acts to apply an elastic force to prevent the cam follower from jumping from the cam.
The operation of the conventional sewing machine shown in FIG. 4 is described from now on. When torque is applied to the main shaft 1 by the motor not shown in the drawing, the shaft is rotated and the torque thereof is transmitted to the sections of the machine trough mechanisms coupled to the shaft. At the left-hand end of the main shaft 1, the vertical motion of the needle rod 13 and that of the thread take-up lever 14 are caused through the needle rod and thread take-up mechanism 12. At the central portion of the main shaft 1, the torque thereof is transmitted to the vertical shaft 15 through the engagement of the bevel gears 2 and 3, and the torque of the vertical shaft is transmitted to the lower shaft 18 through the engagement of the bevel gears 16 and 17 to rotate the shuttle hook 19. The rotation of the eccentric wheel 4 is converted into the vertical motion of the rod 49b through the reciprocative motion of the rod 5, the swing motion of the driving lever 45 and that of the driven lever 49a. The rotation of the eccentric wheel 6 is converted into the reciprocative motion of the rod 7, which causes the swing motion of the upper feed horizontal motion shaft 38 through the upper feed quantity controller 20. The swing motion of the shaft 38 causes that of the horizontal driving lever 40 and the horizontal motion of the upper feed dog 55 through the engagement of the two-split output portion 38o of the shaft and the member 39. Since the two-split front portion of the upper feed dog 55 is engaged with the cam follower 50 rotatively coupled to the lower portion of the rod 49b, the dog performs a vertical motion synchronized with the horizontal motion of the dog, so that the upper feed teeth 57 performs a pseudo-elliptic feed motion. The rotation of the eccentric wheel 8 is converted into the reciprocative motion of the rod 9 and the swing motion of the feed vertical motion shaft 62, and causes the vertical motion of the member 60 rotatively coupled to the output portion 62o of the shaft. The rotation of the eccentric wheel 10 is converted into the reciprocative motion of the rod 11, which causes the swing motion of the lower feed horizontal motion shaft 58 through the lower feed quantity controller 29 so that the horizontal motion of the feed dog 59 coupled to the output portion 58o of the shaft. Since the two-split front portion of the dog 59 is engaged with the member 60, the dog performs a vertical motion synchronized with the horizontal motion thereof, so that feed teeth 75 perform a pseudo-elliptic feed motion. Since it is well known that the above-mentioned motions caused through the rotation of the main shaft 1 are organically synchronized with each other, it is not described in detail herein.
The quantity of an upper feed is controlled by swinging the upper feed control lever 25 to change the posture thereof. The quantity of a lower feed is controlled by swinging the lower feed control lever 34 to change the posture thereof. Mechanisms for changing the postures of the control levers 25 and 34 and mechanisms for maintaining the postures are not shown in the drawings.
Although lower feed mechanisms shown in FIGS. 4 and 5 differ from each other in the form of the feed dog 59 and that of the vertical driving lever 63, the mechanisms are nearly the same as each other in the operation of each portion thereof.
Although the operation of the lower feed horizontal motion shaft 58 of a lower feed mechanism shown in FIG. 6 is the same as that of the lower feed horizontal motion shaft 58 of the lower feed mechanism shown in FIG. 4, the lower feed vertical motion shaft 62 of the mechanism shown in FIG. 6 performs a rotary motion so that the cam 63 mounted on the shaft at the tip thereof is rotated. Since the cam follower 60 mounted on the feed dog 59 at the tip thereof in the lower feed mechanism shown in FIG. 6 is urged by the spring 67 so as to be engaged with the surface of the cam 63, the feed dog performs a vertical motion due to the rotation of the cam. Since the swing motion of the lower feed horizontal motion lever 68 and the rotary motion of the cam 63 in the mechanism shown in FIG. 6 are synchronized with each other as well as those in the mechanism shown in FIG. 4, feed teeth 75 perform a pseudo-elliptic feed motion.
FIG. 7 is an enlarged partial view of another conventional differential vertical sewing machine in which a rotary shaft is provided instead of a vertically moving shaft, a cam is mounted on the rotary shaft at the tip thereof, a sliding block is provided to be guided by the body of a head so as to be straightly moved vertically and is engaged with the cam so as to perform the vertical motion, and feed teeth perform a vertical motion due to that of the block. The upper feed mechanism of the sewing machine is described from now on. In the mechanism, timing pulleys 4 and 8 are mounted on the central portion of a main shaft 1, a member 39 is rotatively coupled to the input end of a horizontal driving lever 40 and engaged with the two-split output portion 38o of an upper feed horizontal motion shaft 38, and a guide 41 provided at the output end of the shaft guides a driven lever 49 to move the lever straightly. A timing pulley 42 is mounted on the input portion of an upper feed vertical motion shaft 43 rotatably supported by bearings 43a and 43b, and is coupled to the timing pulley 4 by a timing belt 5. A cam 44 is mounted on the upper feed vertical motion shaft 43 at the output end thereof. A slider 45 is straightly moved vertically while being guided by a linear guide 48 secured to the head body 53. A cam follower 46 is attached to the upper arm of the slider 45 and engaged with the cam 44 by the elastic force of a spring 47. The slider is restricted by a means not shown in FIG. 7, so that the slider does not rotate about the axis of the straight motion thereof. The driven lever 49 is guided by the guide 41 at the output end of the horizontal driving lever 40. A cam follower 50 is attached to the driven lever 49 at the upper end thereof and engaged with the slider 45 by the upward elastic force of a spring 51 provided between the upper arm 49s of the driven lever and the guide 41. An upper feed dog 55 is rotatively coupled at the rear end thereof to the driven lever 49 at the lower end thereof and guided by an upper feed rest guide 56 rotatably supported by a block attaching rod 52 at the lower end thereof, so that the rest is slid. The rod 52 receives a downward elastic force from a spring 54 provided between the arm 52s of the rod and the head body 53, so that a presser not shown in FIG. 7 is usually at a standstill in contact with a needle plate not shown in FIG. 7. The upper arm 52p of the rod 52 is for lifting the lower arm 45o of the slider 45 when the rod is lifted by a lifter not shown in FIG. 7. The lower feed mechanism of the sewing machine is described from now on. In the mechanism, a lower feed vertical motion shaft 62 is rotatably supported by bearings 62a and 62b. A timing pulley 61 is mounted on the shaft 62 at the input end thereof and coupled to the timing pulley 8 by a timing belt 9. A cam 63 is mounted on the shaft 62 at the output end thereof. A slider 64 is straightly moved vertically while being guided by a linear guide 66 secure to the head body 53. A cam follower 60 is attached to the slider 64 at the upper portion thereof and engaged with the cam 63 by the elastic force of a spring 67 provided between the arm 64s of the slider at the lower end thereof and the linear guide 66. The slider 64 is restricted by a means not shown in FIG. 7, so that the slider does not rotate about the axis of the straight motion thereof.
FIG. 8 shows the case that the cam 63 is composed of a main cam 63a for causing the slider 64 to perform a desired motion, and an auxiliary cam 63b for preventing the cam follower 60 from jumping from the main cam. In that case, the cam follower 60 is engaged with the main cam 63a and attached to the slider 64, and another cam follower 74 is engaged with the auxiliary cam 63b and attached to the slider. The two cam followers 60 and 74 do not separate from the main and the auxiliary cams 63a and 63b due to the phase of the cam 63.
The operation of the sewing machine shown in FIG. 7 is described from now on. The motion of the needle rod and thread take-up mechanism 12 of the machine and the motion of the shuttle hook 19 thereof are the same as those of the sewing machine shown in FIG. 4. The torque of the main shaft 1 of the machine shown in FIG. 7 is transmitted to the upper feed vertical motion shaft 43 through the timing pulley 4, the timing belt 5 and the timing pulley 42 so that the cam 44 mounted on the shaft is rotated. The torque of the cam 44 acts through the cam follower 46 so that the slider 45 is straightly moved vertically while being guided by the head body 53, and the driven lever 49, which is coupled at the upper end thereof with the bottom of the slider through the cam follower 50 and guided by the guide portion 41 of the horizontal driving lever 40 so as to be straightly moved, is moved vertically. The torque of the main shaft 1 acts through an eccentric wheel 6, a rod 7 and an upper feed quantity controller 20 to swing an upper feed horizontal motion shaft 38 whose swing motion is converted into that of the horizontal driving lever 40 through the engagement of the two-split output end portion 38o of the upper feed horizontal motion shaft and the member 39 rotatively coupled to the lever. The swing motion of the lever 40 acts to swing the driven lever 49 which is guided by the guide portion 41 of the horizontal driving lever 40. Thus, the driven lever 49 performs both the vertical motion and the swing motion because of the torque of the main shaft 1. For that reason, the upper feed dog 55 rotatively coupled at the rear end thereof to the driven lever 49 at the lower end thereof and guided for sliding, at the front portion of the dog by an upper feed rest guide 56 rotatably supported by the block attaching rod 52 performs a horizontal motion and a swing motion so that upper feed teeth 57 attached to the bottom of the front portion of the dog perform a pseudo-elliptic feed motion. In the upper feed mechanism, the direction of the vertical motion of the driven lever 49 is reverse to that of the vertical motion of the upper feed teeth 57. In other words, the teeth 57 are moved down when the lever 49 is moved up. When the block attaching rod 52 is pushed up in the upper feed mechanism by a push-up means not shown in FIG. 7, the upper feed dog guide 56 is moved up so that the upper feed teeth 57 are moved up. In that case, since there is a gap between the upper arm 52p of the lifter attaching rod 52 and the lower engaging portion 45o of the slider block 45 as the rod is moved down, the upper feed dog 55 is rotated counterclockwise at the time of the upward motion of the rod. For that reason, when the rod 52 is pushed up, the bottoms of the upper feed teeth 57 are moved up to a position above that of the bottom of the presser not shown in FIG. 7. The horizontal motion of the lower feed mechanism of the sewing machine shown in FIG. 7 is the same as that of the lower feed mechanism of the sewing machine shown in FIG. 4. The torque of the main shaft 1 is transmitted to the lower feed vertical motion shaft 62 through the timing pulley 8, the timing belt 9 and the timing pulley 61 so that the cam 63 mounted on the shaft at the tip thereof is rotated. The torque of the cam 63 acts through the cam follower 60 so that the slider 64 is straightly moved vertically while being guided by the head body 53, and the front portion of the lower feed dog 59 fitted at the front end 59o thereof with a plurality of cam followers 65 engaged with the upper arm 72 of the slider 64 on the top and bottom of the arm is moved vertically. Since a horizontal motion is transmitted to the lower feed dog 59 at its rear end rotatively coupled to a lower feed horizontal motion lever 68, the lower feed teeth 75 attached to the top of the central portion of the dog perform a pseudo-elliptic feed motion.
In the case shown in FIG. 8, the cam 63 is composed of the main cam 63a as the body of the cam and the auxiliary cam 63b for preventing the main cam from jumping from the cam follower, one 60 of the plural cam followers 60 and 74 attached with a gap therebetween to the slider 64 is in contact with the main cam, and the other 74 of them is in contact with the auxiliary cam. Since the auxiliary cam 63b is shaped so that the plural cam followers 60 and 74 located at a prescribed distance from each other are always simultaneously in contact with the main cam 63a and the auxiliary cam, regardless of the phase of the cam 63, the cam followers 65 do not jump even if the rotation speed of the cam increases. Since the slider is disposed between the cam and the feed dog in the case shown in FIG. 8, the cam followers 60 and 74 are not moved in directions C and D as the feed dog is moved in the directions.
FIG. 9 shows the eccentric wheels, the rod and the vicinity of them in each of the conventional sewing machines shown in FIGS. 4 and 7. The eccentric wheel 101, which is denoted by 8 in FIG. 4 and by 10 in FIG. 7, is secured to the main shaft 1 by a screw 102, and the rod 103, which is denoted by 9 in FIG. 4 and by 11 in FIG. 7, is rotatively coupled to the wheel. When the main shaft 1 shown in each of FIGS. 4 and 7 is rotated, the eccentric wheel 101 secured to the shaft is rotated so that the rod 103 is swung in directions C and D and directions A and B, or, to be exact, the center of the ring of the rod at the upper end thereof performs a circular motion and the tip of the rod, which is not shown in FIG. 9, is moved in the directions A and B.
FIG. 10 shows the vertical motion of the feed teeth 27, which is caused by the above-mentioned motion of the tip of the rod 103, in the sewing machine shown in FIG. 4 and not having a cam unit. FIG. 11 shows the vertical motion of the feed teeth 75, which is caused by the above-mentioned motion of the tip of the rod 103, in the sewing machine shown in FIG. 7 and having the cam unit.
FIG. 10 shows the vertical motion of the feed dog 59 and the feed teeth 75 in their elliptic motion during the sewing operation of the sewing machine shown in FIG. 4 and not having the cam unit. In FIG. 10, the axis of abscissas and that of ordinates denote the rotation angle .theta. of the main shaft 1 and the vertical position h of the feed teeth 75, respectively. The motion of the feed teeth 75 during the single round of the rotation of the msin shaft 1 or during a single stitch is denoted by a curve P.fwdarw.Q.fwdarw.R.fwdarw.S.fwdarw.T shown in FIG. 10. A point P or T shown in FIG. 10 indicates the bottom dead point of the feed teeth 75. A point R shown in FIG. 10 indicates the top dead point of the feed teeth 75. A point Q shown in FIG. 10 indicates the instant at which the feed teeth 75 come up out of a needle plate not shown in the drawings or the teeth collide against a presser. A point S shown in FIG. 10 indicates the instant at which the feed teeth 75 go into the needle plate or the teeth separate from the presser. As mentioned above, the feed teeth 75 collide against the presser at the point Q at which the phase of the main shaft 1 is .theta.Q, and the teeth separate from the presser at the point S at which the phase of the main shaft is .theta.S. The larger the angle .alpha. between the tangent on the curve and the positive direction of the axis of abscissas is, the higher the speed of the vertical motion of the feed teeth 75 is. As understood from FIG. 10, the feed teeth 75 collide against the presser at the time of the maximum speed of the upward motion of the teeth.
FIG. 11 shows the vertical motion of the feed dog 59 and the feed teeth 75 in their elliptic motion during the sewing operation of the sewing machine shown in FIG. 7 and having the cam unit. The axis of abscissas and that of ordinates shown in FIG. 11 denote the rotation angle .theta. of the main shaft 1 and the vertical position h of the feed teeth 75, respectively. Symbols shown in FIG. 11 denote the same as those in FIG. 10 except symbols A, B, C and D. The vertical motion of the feed teeth 75 is denoted by a curve P.fwdarw.Q.fwdarw.R.fwdarw.S.fwdarw.T shown in FIG. 11. The speed of the vertical motion of the feed teeth 75 is zero (.alpha.=0) at a point Q at which the teeth collide against a presser, and at a point S at which the teeth separate from the presser. The feed teeth 75 are moved up at a prescribed speed toward the collision point Q, and moved up at a sharply decreasing speed in the immediate vicinity of the collision point. The speed of the upward motion of the teeth 75 instantaneously becomes zero at the time of the arrival at the collision point Q. Immediately after the arrival at the collision point Q, the teeth 75 are moved up further while the speed thereof increases gradually. At a point H or R indicating the top dead point of the motion of the teeth 75, the teeth begin to be moved down. The speed of the downward motion of the teeth 75 instantaneously becomes zero at a point S due to an action reverse to that in the above-mentioned upward motion of the teeth, so that the teeth are put out of contact with the presser. Such operation is repeated to feed a sewn object.
In the sewing machines employing the cam units shown in FIGS. 6 and 8, it is enabled by appropriately predetermining the form of the cam that the feed teeth 75 are caused to perform the motion shown in FIG. 11. For the motion, the cam has such a form that the speed of the collision of the feed teeth 75 with the presser is approximate to zero. When the lower feed horizontal output lever 68 is swung in the directions A and B in the sewing machine shown in FIG. 6, the cam follower 60 is moved in the directions C and D so that the cam follower deviates from a vertical line .lambda.-.lambda.' extending through a cam shaft 62. For that reason, it is complicated to design the form of the cam 63. This is a problem. Besides, it is geometrically difficult to provide a positive cam. This is also a problem. The sewing machine shown in FIG. 8 was developed as one of means for solving the problems. However, since the sliding block 64 is added to prevent the cam follower 74 from deviating the vertical line .lambda.-.lambda.', the sewing machine is complicated.
Since the conventional sewing machines are constituted as described above, the vertical motion shaft 62 needs to be rotated if the cam unit is provided to reduce the speed of the collision of the feed teeth 75. This is a problem. If a positive cam such as the lower feed vertical motion cam 63 is provided to prevent a cam follower from jumping from the cam when the cam is rotated rapidly, the cam follower 65 and the slider 64, which are moved straightly, need to be provided so that the constitution of the machines is complicated. This is also a problem.